Although I'm a huge fan of RealTracks, I'd also like to see the MIDI equivalent of RealTracks. That is, instead of pulling up complete styles, I'd like to be able to select MIDI tracks the same as RealTracks.
I'd think that most of the piano styles in the "Piano Pop" (set 70) and "LitePop" (set 84) would work well as MIDI. P_JONI seems to be about all I've been able to find on the MIDI styles. Similarly, many of the RealTrack bass styles should also work as MIDI.
I think RealTracks have shown that being able to create an arrangement via "mix and match" is a viable approach. While it's possible to create new styles which are a mix of existing styles, there's a real convenience of being able to select a single track via the RealTracks browser.